The demonstration that recombinant tissue plasminogen activator (rtPA) is useful for acute management is changing the approach to ischemic stroke. However, after more than a decade, the use of tPA therapy remains limited. Several factors could contribute to this limitation: irreversible cell damage induced by cerebral ischemia over time;the profile of rtPA treated patients at high risk of hemorrhagic transformation;and the potential detrimental effects of rtPA. Combination pharmacotherapy strategies to expand the rtPA fibrinolysis time window beyond 3 hours are under active investigation. In principle, it may be possible to extend the therapeutic window for rtPA therapy by using a neuroprotective drug. Estrogen is well known to diminish the neurotoxicity caused by NMDA activation. Preliminary evidence is presented in this proposal showing that 17[unreadable]-estradiol stabilizes blood brain barriers (BBB) against cerebral ischemia reperfusion injury through inhibition of matrix metalloproteinase 2 and 9 (MMP2, MMP9) activation, the major factors related to hemorrhagic transformation. 17[unreadable]-estradiol attenuates rtPA induced MMP2 and MMP9 activation in primary astrocytes. Most importantly, we have demonstrated that 17[unreadable]-estradiol extends the therapeutic window of rtPA upon pretreatment in female rats in an embolic middle cerebral artery occlusion (MCAO) model. Thus, the protective properties of estrogen make it a good candidate for combination therapy with rtPA. The neuroprotective effects of estrogen could delay irreversible cell damage. Further, estrogen may attenuate the side effects of rtPA, thereby prolonging the therapeutic window of rtPA and greatly broaden its clinical application. The present application will test the hypothesis that 17[unreadable]-estradiol extends therapeutic window of rtPA in embolic stroke, and determine the underlain mechanisms. To achieve these objectives, the following specific aims will be addressed. 1) To assess the interaction of estrogen and rtPA on glutamate neurotoxicity and matrix metalloproteinases (MMPs) activation. 2) To determine if 17[unreadable]-estradiol extend the therapeutic window of rtPA in female rats in an embolic stroke model. 3) To determine if 17[unreadable]-estradiol extend the therapeutic window of rtPA in male rats in an embolic stroke model. The application's objectives are to explore the feasibility for further clinical trials of combination therapy of estrogen and rtPA for ischemic stroke.The demonstration that recombinant tissue plasminogen activator (rtPA) is useful for acute management is changing the approach to ischemic stroke. However, after more than a decade, the use of rtPA therapy remains limited and has had only a modest impact in the overall burden of ischemic stroke. Several factors could contribute to this limitation: irreversible cell damage induced by cerebral ischemia over time;the profile of rtPA treated patients at high risk of hemorrhage;and the potential side effects of rtPA. Combination pharmacotherapy strategies to expand the 3 hour therapeutic window rtPA are under active investigation. In principle, it may be possible to extend the therapeutic window for rtPA therapy by using a neuroprotective drug. Preliminary evidence is presented in this proposal showing that estrogen can protect against ischemic stroke, and potentially attenuate side effect of rtPA. The present application will test the hypothesis that 17[unreadable]-estradiol extends therapeutic window of rtPA in embolic stroke, and determine the underlain mechanisms. The application's objectives are to explore the feasibility for further clinical trials of combination therapy of estrogen and rtPA for ischemic stroke.